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Summa Phytopathologica

versão impressa ISSN 0100-5405versão On-line ISSN 1980-5454

Resumo

CAMARA, Guilherme de Resende; BUSATO, Laedio Magno; ALMEIDA, Bárbara Favalessa  e  MORAES, Willian Bucker. Elaboration and validation of diagrammatic scale for lettuce powdery mildew. Summa phytopathol. [online]. 2018, vol.44, n.2, pp.116-121. ISSN 0100-5405.  https://doi.org/10.1590/0100-5405/175851.

Powdery mildew, caused by Oidium sp., is a disease of great importance in hydroponic crops of lettuce. However, in Brazil, there is scarce research focused on the epidemiological study of this disease, as standardized methods are necessary to quantify the disease severity in hydroponic systems. Thus, a logarithmic scale was developed at levels of 0.37, 1, 2, 4, 8, 16, 32 and 74% injured leaf area, testing the parameters accuracy and precision. The proposed scale was validated by eight evaluators, of whom four were experienced and four were inexperienced, and they used 50 leaves showing symptoms of the disease at different severity levels, previously measured with the aid of QUANT® software. Two evaluations were performed with a 48-h interval, in which the evaluators visually estimated distinct sequences of leaves. Linear regression was used to determine the accuracy and the precision of each evaluator. The proposed scale showed satisfactory results of accuracy and precision, and despite the inexperience of four evaluators, absolute errors were in the range of 8% after training. The proposed scale was adequate to estimate the severity of powdery mildew on lettuce.

Palavras-chave : Oidium sp; Lactuca sativa L.; severity; epidemiology.

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